[0001] The present invention relates to a method for manufacturing a composite and to a
wind turbine blade. The invention especially relates to a method for manufacturing
a wind turbine blade.
[0002] Modern wind turbine blades are typically manufactured using Vacuum Assisted Resin
Transfer Moulding, a process that produces strong, lightweight composites by infusing
resin into compacted reinforcing materials under vacuum. A large part of reinforcing
material is usually glass or carbon fibre woven mats.
[0003] For deeply concave shapes of the inner face of the mould there may be the risk that
the fibre mats are not maintained in a position firmly against the mould during lay-up.
Instead of following the actual curvature of the mould the fibre mats may in certain
circumstances tend to take on the shape of catenaries (like a hanging chain), leaving
voids between the inner surface of the mould and the fibre mats ("hovering glass").
If several layers of fibre mats are placed on top of each other, friction between
the layers may be strong enough to prevent the fibre mats from being pressed against
the mould when vacuum is applied. In the subsequent moulding process the voids between
the surface of the mould and the fibre mats will be filled with resin that is not
reinforced by any fibre material. As a result, the structural characteristics of the
blade in the regions of "hovering glass" may not be as desired.
[0004] In addition, if on application of vacuum the glass is pressed partly or completely
out into the void this may result in wrinkles and folds of the fibre mats, which may
in turn lead to mechanical weaknesses if the wrinkles and folds are not flattened
before the resin is injected.
[0005] In
US 2003/0077965 A1 a three-dimensional spacer fabric resin infusion medium and reinforcing composite
lamina for use in the manufacture of fibre reinforced polymer composites is disclosed.
The use of the three-dimensional spacer fabric as a composite lamina aids in both
the resin infusion rate and resin uniformity throughout the laminate.
[0006] In
WO 2007/038930 A1 a Resin Transfer Moulding method of producing a fibre reinforced product is disclosed.
The method comprises the steps of: a) placing at least one porous member in a mould;
b) placing one or more layer(s) of reinforcing fibres in the mould; c) introducing
resin for distribution through the porous member to the fibre layers; and d) allowing
the resin to cure and the distribution member to coalesce to form a continuous layer.
[0007] In
EP 1 310 351 B1 a method for making a windmill blade of composite materials which include a fibre
reinforced matrix material is disclosed, wherein the blade is made in one piece in
a closed mould. The method comprises the following steps: A mould core with a flexible
external core part and an internal, firm or workable core part, and outer mould parts
are arranged to close around the mould core for formation of a mould cavity there
between. Composite material and possible core inserts are laid on an outer mould part
and/or the mould core. The outer mould parts are closed around the mould core and
around the composite material placed in the mould cavity. The composite material is
set. The outer mould parts are removed. The mould core is taken out of the shape permanent
blade before or after removing the outer mould parts. Some of the required matrix
material is used in connection with the reinforcing fibre when laying the composite
material and where additional matrix material is added after closing the mould. The
method involves use of composite materials such as glass or carbon fibre reinforced
epoxy, polyester, vinyl ester, or thermoplastic.
[0008] It is a first objective of the present invention to provide a method for manufacturing
a composite, wherein "hovering glass" and folds during the manufacture of the composite
in deeply concave moulds are avoided. It is a second objective of the present invention
to provide an advantageous wind turbine blade.
[0009] The first objective is solved by a method for manufacturing a composite as claimed
in claim 1. The second objective is solved by a wind turbine blade as claimed in claim
14. The depending claims define further developments of the invention.
[0010] The inventive method for manufacturing a composite comprises the steps of: laying
at least one fibre mat onto the inner surface of a mould; applying suction between
the inner surface of the mould and the at least one fibre mat; covering the outermost
fibre mat of the at least one fibre mat with at least one vacuum bag; introducing
vacuum to the region between the vacuum bag and the mould; injecting resin under vacuum
into the region between the vacuum bag and the mould; letting the resin set; and removing
the mould.
[0011] The idea of the invention is to apply suction between the inner surface of the mould
and the fibre mats during lay-up. This means, that suction is applied between the
inner surface of the mould before the outermost fibre mat of the at least one fibre
mat is covered with at least one vacuum bag. The suction will force the fibre mats
to flatten against the inner surface of the mould. By this means "hovering glass"
and folds during the manufacture of the composite, especially in deeply concave moulds,
are avoided effectively.
[0012] The outermost fibre mat of the at least one fibre mat may be covered with a mould
core which is covered by at least one vacuum bag such that the vacuum bag is placed
on the outermost fibre mat. This can advantageously be done before introducing vacuum
to the region between the vacuum bag and the mould.
[0013] Moreover, a medium which is suitable to distribute vacuum can be placed between the
inner surface of the mould and the at least one fibre mat and/or between two subsequent
fibre mats. This medium which is suitable to distribute vacuum may be used for applying
suction between the inner surface of the mould and the at least one fibre mat. In
the context of the present invention the medium which is suitable to distribute vacuum
is also denoted as a vacuum distributing medium. This vacuum distributing medium may
be placed on the inner surface of the mould. One or two layers of fibre material may
be placed on top of the vacuum distributing medium. When air is pumped out of the
vacuum distributing medium, suction will force the medium to flatten against the inner
surface of the mould, and at the same time the layers of fibre material will be sucked
in towards the vacuum distributing medium. Because the fibre material is not airtight,
subsequent layers of fibre material placed on top of the existing ones will also experience
suction, and thus be forced to lie flat against the mould.
[0014] A medium which is suitable to distribute vacuum, i.e. a vacuum distributing medium,
can be used which is impregnable by resin. In this case the vacuum distributing medium
can become an integrated part of the laminate. Otherwise the surface of the composite,
for example the surface of a wind turbine blade, might peel away.
[0015] If necessary, wrinkles and folds in one layer of fibre mats can be removed manually
before the next layer is put into place. Once wrinkles and folds have been removed,
suction will keep the layers flat.
[0016] Advantageously, a layer of material which has a lower air permeability than the fibre
mat may be placed on top of the outermost fibre mat. A material which has a lower
air permeability than the fibre mat can be used which is suitable for lamination.
In this case also the material which has a lower air permeability than the fibre mat
can become an integrated part of the laminate. Generally, placing a layer of material
which has a lower air permeability than the fibre mat on top of the outermost fibre
mat increases the suction that holds the fibre mats in place.
[0017] For example, once all fibre and possibly other core materials have been put in place,
a single layer of material which has a low air permeability can be placed on top in
order to increase the suction that holds the core materials in place. In case of the
manufacturing of a wind turbine blade the layer of low air permeability, especially
of a lower air permeability than the used fibre mat, can advantageously be suitable
for lamination because a shear web can be placed on this layer. In this case it is
essential that a strong bond is formed between the shear web and the rest of the laminated
blade.
[0018] Generally, the fibre material is not airtight and the difference in pressure between
the two sides of a layer, for example of a fibre mat, is small. However, because the
fibre material is very flexible, the small pressure difference is sufficient to keep
the fibre material in place.
[0019] Generally, the inventive method may be used to manufacture a wind turbine blade.
In this case the composite may be a wind turbine blade and the method may comprise
the steps of laying at least one fibre mat onto a concave inner surface of a lower
and of an upper part of a mould, applying suction between the inner surface of at
least one of the mould parts and the at least one fibre mat, covering the outermost
fibre mat laying in the lower part of the mould with a mould core which is covered
by at least one vacuum bag such that the vacuum bag is placed on the outermost fibre
mat, placing the upper part of the mould on top of the lower part of the mould such
that the mould is closed, introducing vacuum to the region between the vacuum bag
and the mould, injecting resin under vacuum into the region between the vacuum bag
and the mould, letting the resin set, and removing the mould and the mould core. By
means of this method the wind turbine blade can be manufactured in one piece without
glued joints. Preferably the upper part of the mould can be turned around its longitudinal
axis before placing it on top of the lower part of the mould.
[0020] The medium which is suitable to distribute vacuum can be placed between the inner
surface of the upper and/or lower part of the mould and the fibre mat. The medium
which is suitable to distribute vacuum may also be placed between two subsequent fibre
mats.
[0021] Additionally, a core material can be placed between subsequent fibre mats. The core
material may also be used as the medium which is suitable to distribute vacuum. Furthermore,
at least one shear web can be placed onto the outermost fibre mat laying in the lower
part of the mould.
[0022] Preferably at least one fibre mat which is placed in the lower part of the mould
can overlap with at least one fibre mat which is placed in the upper part of the mould.
Additionally or alternatively, at least one fibre mat which is placed in the upper
part of the mould can overlap with at least one fibre mat which is placed in the lower
part of the mould. This overlap increases a stability of the joint between the two
halves of the finished blade. Advantageously, a biaxial fibre mat can be used as the
fibre mat which overlaps with at least one fibre mat of the upper or lower part of
the mould.
[0023] For example, the upper and the lower part of the mould can be filled with fibre and
core materials while positioned with the inner, concave faces facing upwards. The
fibre and core materials can be placed in both parts of the mould under suction as
described above. Next the shear web, the mould cores and the vacuum bags can be placed
in the lower part of the mould. The upper part of the mould can then be turned 180°
around its longitudinal axis and placed on top of the lower part such that the mould
is closed. Because of the low weight of the fibre material and the core material the
small pressure difference across the outermost layer of low air permeability, which
means that the air permeability is lower than that of the fibre mats, is sufficient
to hold the core materials in place during this turning process. The weight of the
fibre and core material is typically less than 10g/cm
2 to 20g/cm
2, which means that a pressure difference of a few percent of atmospheric pressure
is sufficient.
[0024] It is important that some of the layers of fibre material placed in the lower part
of the mould overlap with some of the layers placed in the upper part of the mould
when the two parts are assembled. Otherwise the joint between the two halves of the
finished blade would consist purely of cured resin without any form of fibre reinforcement.
Such a joint would be weaker than desired.
[0025] Generally, placing a vacuum distributing layer on or in the immediate vicinity of
the inner surface of the mould and pumping air out of this vacuum distributing layer
during the draping of the fibre mats will result in the fibre mats being sucked in
towards the inner face of the mould such that no "hovering glass" and no wrinkles
or folds are left in the fibre glass when resin injection is initiated.
[0026] The fibre mats may consist of glass or carbon fibre woven mats.
[0027] The inventive wind turbine blade with a laminated structure comprises at least one
layer of unidirectional fibre glass, at least one layer of biaxial fibre glass, and
at least one layer which was suitable to distribute vacuum before it was laminated.
The layer which was suitable to distribute vacuum before it was laminated may comprise
core material.
[0028] Further features, properties and advantages of the present invention will become
clear from the following description of an embodiment in conjunction with the accompanying
drawings. All described features are advantageous separate and in combination with
each other.
- Fig. 1
- schematically shows a cross section of an assembled mould for manufacturing a wind
turbine blade according to the state of the art.
- Fig. 2
- schematically shows a cross section of part of an upper and part of a lower mould
during the assembling process according to the present invention.
- Fig. 3
- schematically shows an alternative variant of the lay-up of different layers.
[0029] An embodiment of the present invention will now be described with reference to figures
1 to 3. Figure 1 schematically shows a cross section of an assembled mould according
to
EP 1 310 351 B1. The first step in the manufacturing process according to
EP 1 310 351 B1 is to fill the lower part of the mould 1 with layers 2 of fibre glass and core material
like balsa wood. The mould cores 3A and 3B are covered by vacuum bags 5A and 5B and
placed in the mould together with a shear web 4. Then more fibre glass and core material
6 is placed over the mould cores, and the upper part of the mould 7 is put into place.
Vacuum is introduced to the region between the vacuum bags 5A, 5B and the mould 1,
and resin is injected into the core material under vacuum.
[0030] Figure 2 schematically shows a cross section of part of an upper 7 and part of a
lower 1 mould during the assembling process. It illustrates the method for manufacturing
a wind turbine blade according to the present invention. What is shown is an enlargement
of a cross section of a portion of the mould, the portion within the circle in figure
1, just before the upper and lower parts of the mould 1, 7 are assembled. Figure 2
only illustrates the lay-up process and the assembly of the mould parts at the leading
edge of the blade. The processes at the trailing edge are similar and will not be
detailed here.
[0031] A vacuum distributing layer 10 is placed on the inner surface of both the upper 7
and lower 1 part of the mould. The vacuum distributing layer 10 is connected to a
vacuum pump 8 for applying suction. A layer of biaxial fibre glass 11 is placed on
the inner surface of the vacuum distributing layer 10 and one or more layers of unidirectional
fibre glass mats 12 are added, together with a layer of core material 13 like balsa
wood. During the lay-up of the layer of biaxial fibre glass 11, the layers of unidirectional
fibre glass mats 12 and the layer of core material 13 suction is applied between the
inner surface of the mould parts 1, 7 and the layers 11, 12, 13 by means of the vacuum
distributing layer 10.
[0032] On top of the core material 13 one or more additional layers of unidirectional fibre
glass mats 14 are placed. Finally the lay-up is completed with a second layer of biaxial
fibre glass 15. This second layer 15 can be of a non-woven type, which is less permeable
to air, or an additional layer of non-woven fibre glass with a lower air permeability
than the other fibre mats can be placed on top of the second layer of biaxial fibre
glass 15. During the lay-up of the additional layers of unidirectional fibre glass
mats 14 and the second layer of biaxial fibre glass 15 suction is still applied between
the inner surface of the mould parts 1, 7 and the layers 14, 15 by means of the vacuum
distributing layer 10.
[0033] When the lay-up in both parts of the mould has been completed, the mould cores 3A,
3B with the vacuum bags 5A, 5B and the shear web 4 are placed in the lower part 1
of the mould. Because all the layers of fibre material in both parts of the mould,
and particularly those that are in contact with the shear web 4, are suitable for
lamination, the shear web 4 becomes firmly integrated in the laminated blade structure.
[0034] Next, the upper part 7 of the mould is turned 180° around its longitudinal axis and
put into place so that the mould is closed.
[0035] The layers of biaxial fibre glass 11, 15 are intended to provide torsional strength
to the blade and it is therefore essential that a continuous biaxial fibre glass reinforce
laminate is formed around the entire circumference of the blade. The unidirectional
fibre glass mats 12, 14 are intended to provide tensile strength in the longitudinal
direction of the blade. It is therefore not important to have an overlap between the
unidirectional fibre glass mats 12, 14 in the two parts 1, 7 of the mould.
[0036] As can be seen in figure 2 some of the fibre glass mats and core material placed
in the lower part 1 of the mould extend beyond the edge 9 of the lower mould part
1. Alternatively or additionally, some of the fibre glass mats and core material placed
in the upper part 7 of the mould may extend beyond the edge 16 of the upper mould
part 7. During the initial stages of the lay-up this material can be draped over the
edge 9, 16 of the mould 1, 7. Once the mould core 3A is positioned in the mould, those
parts of the fibre glass layers in the lower part of the mould 1, which extend beyond
the edge 9 of the mould and which are not sucked in towards the mould surface, are
positioned against the mould core 3A as shown in figure 2.
[0037] When the two parts of the mould are put together, the layers of biaxial fibre glass
11, 15 in the two parts will overlap and thus a strong joint of laminate between the
two halves of the blade is formed.
[0038] Another variant is schematically shown in figure 3, where the vacuum distributing
medium 18 is not placed directly in the mould 17. Instead a layer of fibre material
19 is placed on the inside surface of the mould 17 and the vacuum distributing medium
18 is placed on top of this layer. In this case the first layer of fibre material
19 is not flattened against the surface of the mould 17 until the vacuum distributing
medium 18 has been put into place, a second layer of fibre material 20 put on top
of it, and a pump 8 connected to the vacuum distributing medium 18. Subsequent layers
of fibre material 21, 22 are placed and flattened as described above.
[0039] In a further variant the core material 13 is used as suction distributing medium
or vacuum distributing medium. This means that the outer layers are not laid up while
suction is applied, but once the core material is placed and suction is applied the
outer layers will be firmly pressed against the mould and new layers on the inside
will also be pressed firmly against the core material.
[0040] Close to the edges of fibre glass lay-up the pressure between the individual layers
is higher than elsewhere. Therefore suction may not be sufficient to prevent the layers
from peeling away from the mould at the edges. To compensate for this the outermost
layer can be chosen to have a higher stiffness than the rest of the layers.
[0041] After covering the outermost fibre mat laying in the lower part 1 of the mould with
the mould cores 3A, 3B which are covered by vacuum bags 5A, 5B such that the vacuum
bags 5A, 5B are placed on the outermost fibre mat 15, 22 and after placing the upper
part 7 of the mould on top of the lower part 1 of the mould such that the mould is
closed, vacuum is introduced to the region between the vacuum bags 5A, 5B and the
mould 1, 7. Then resin is injected under vacuum into the region between the vacuum
bags 5A, 5B and the mould 1, 7. When the resin is set the mould 1, 7 and the mould
core 3A, 3B is removed.
[0042] The present invention effectively prevents the occurrence of folds and "hovering
glass" during the manufacture of composites, especially in deeply concave moulds.
1. A method for manufacturing a composite comprising the steps of:
- laying at least one fibre mat (11, 12, 14, 15, 19-22) onto the inner surface of
a mould (1, 7, 17),
- applying suction between the inner surface of the mould (1, 7, 17) and the at least
one fibre mat (11, 12, 14, 15, 19-22),
- covering the outermost fibre mat (15, 22) of the at least one fibre mat (11, 12,
14, 15, 19-22) with at least one vacuum bag (5A, 5B),
- introducing vacuum to the region between the vacuum bag (5A, 5B) and the mould (1,
7, 17),
- injecting resin under vacuum into the region between the vacuum bag (5A, 5B) and
the mould (1, 7, 17),
- letting the resin set, and
- removing the mould (1, 7, 17).
2. The method as claimed in claim 1, wherein
the outermost fibre mat (15, 22) of the at least one fibre mat (11, 12, 14, 15, 19-22)
is covered with a mould core (3A, 3B) which is covered by at least one vacuum bag
(5A, 5B) such that the vacuum bag (5A, 5B) is placed on the outermost fibre mat (15,
22).
3. The method as claimed in claim 1 or 2, wherein
a medium which is suitable to distribute vacuum (10, 18) is placed between the inner
surface of the mould (1, 7, 17) and the at least one fibre mat (11, 12, 14, 15, 19-22)
and/or between two subsequent fibre mats (11, 12, 14, 15, 19-22) and is used for applying
suction between the inner surface of the mould (1, 7, 17) and the at least one fibre
mat (11, 12, 14, 15, 19-22).
4. The method as claimed in claim 3, wherein
a medium which is suitable to distribute vacuum (10, 18) is used which is impregnable
by resin.
5. The method as claimed in any of the claims 1 to 4, wherein a layer of material which
has a lower air permeability than the fibre mat is placed on top of the outermost
fibre mat (15, 22).
6. The method as claimed in claim 5, wherein
a material which has a lower air permeability than the fibre mat is used which is
suitable for lamination.
7. The method as claimed in any of the claims 1 to 6, wherein the composite is a wind
turbine blade and wherein the method comprises the steps of:
- laying at least one fibre mat (11, 12, 14, 15, 19-22) onto a concave inner surface
of a lower (1, 17) and of an upper part (7, 17) of a mould,
- applying suction between the inner surface of at least one of the mould parts (1,
7, 17) and the at least one fibre mat (11, 12, 14, 15, 19-22),
- covering the outermost fibre mat (15, 22) laying in the lower part (1, 17) of the
mould with a mould core (3A, 3B) which is covered by at least one vacuum bag (5A,
5B) such that the vacuum bag (5A, 5B) is placed on the outermost fibre mat (15, 22),
- placing the upper part (7, 17) of the mould on top of the lower part (1, 17) of
the mould such that the mould is closed,
- introducing vacuum to the region between the vacuum bag (5A, 5B) and the mould (1,
7, 17),
- injecting resin under vacuum into the region between the vacuum bag (5A, 5B) and
the mould (1, 7, 17),
- letting the resin set, and
- removing the mould (1, 7, 17) and the mould core (3A, 3B).
8. The method as claimed in claim 7, wherein
the upper part (7, 17) of the mould is turned around its longitudinal axis before
placing it on top of the lower part (1, 17) of the mould.
9. The method as claimed in claim 3 or 4 in conjunction with claim 7 or 8, wherein
the medium which is suitable to distribute vacuum (10, 18) is placed between the inner
surface of the upper (7, 17) and/or lower part (1, 17) of the mould and the fibre
mat (11, 12, 14, 15, 19-22), and/or between two subsequent fibre mats (11, 12, 14,
15, 19-22).
10. The method as claimed in any of the claims 1 to 9, wherein
a core material (13) is placed between subsequent fibre mats (11, 12, 14, 15, 19-22).
11. The method as claimed in any of the claims 7 to 10, wherein
at least one shear web (4) is placed onto the outermost fibre mat (15, 22) laying
in the lower part (1, 17) of the mould.
12. The method as claimed in any of the claims 7 to 11, wherein
at least one fibre mat (11, 12, 14, 15, 19-22) which is placed in the lower part (1,
17) of the mould overlaps with at least one fibre mat (11, 12, 14, 15, 19-22) which
is placed in the upper part (7, 17) of the mould and/or at least one fibre mat (11,
12, 14, 15, 19-22) which is placed in the upper part (7, 17) of the mould overlaps
with at least one fibre mat (11, 12, 14, 15, 19-22) which is placed in the lower part
(1, 17) of the mould.
13. The method as claimed in claim 12, wherein
a biaxial fibre mat (11, 15) is used as the fibre mat which overlaps with at least
one fibre mat of the upper (7, 17) or lower (1, 17) part of the mould.
14. A wind turbine blade with a laminated structure comprising at least one layer of unidirectional
fibre glass (12, 14), at least one layer of biaxial fibre glass (11, 15) and at least
one layer which was suitable to distribute vacuum (10, 18) before it was laminated.
15. The wind turbine blade as claimed in claim 14, wherein the layer which was suitable
to distribute vacuum (10, 18) before it was laminated comprises core material (13).